Great! But, how does that link indicate that what can be seen on my picture is a phone connection?
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StackedCrookedAug 5 '12 at 18:25

It probably is a phone socket, but it looking at the photo, it doesn’t look like there’s anywhere for the four pins to go in, let alone the fifth. Surely it’s the back and the other side is in another room.
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SynetechAug 5 '12 at 18:42

I’m not familiar with outlets in Belgium, but assuming they are typical European outlets, then it looks to be a high-voltage stove/oven or dryer electrical outlet (why it would be in the living room though is beyond me).

The labels for the four connectors (a, b, S, ground) are curious, but presumably they are hot (a), hot (b), neutral (S), and ground:

There are also two other connectors (c, d here) which are specifically part of a stove/oven outlet as opposed to a dryer outlet: